Yellow leaf and harvest time

Dried burned upard tips is usually nutrition burn. Ph issues and not enough run off can easily contribute to these. I experienced them myself and had to correct the problems. As far as harvest. Not sure on what week your on, but guessing 1 more of feed then two for flush and fade. Best to get a 60x jeweler's eye. Look at trichromes on buds in several spots. When mass majority is milky white is when you should make 2 week run to harvest. Good luck and hope this helps. Send me a message if you need further information. 🌲🌲🌲👊